The present invention is in the field of optical fibers or xe2x80x9clight pipesxe2x80x9d that carry signals and information in the form of light, and more particularly in the field of devices used to precisely terminate and mount the ends of such fibers.
Optical fibers are now commonly used to transmit light signals from one place to another for a variety of reasons. They may communicate an optical signal from an optical source to an optical sensor on a circuit board to turn transistors on and off. Optical fibers may also be used to sense the presence or absence of an opaque object in a gap between two aligned fiber ends, such that light is freely transmitted from one fiber end to another across the gap to complete a circuit when the object is absent, and light is blocked to break the circuit when the object is present. These are but two examples of many possible uses for optical fibers.
It is generally necessary to cleanly terminate and accurately mount the ends of optical fibers in order to maintain good light transmission quality from the terminated end to the receiving fiber or device. It is also important to mount the terminated fiber ends securely to maintain the accuracy and quality of signal transmission, especially in environments subject to vibration and/or tension such as vehicle wiring systems.
One common technique for terminating and mounting optical fiber ends is with externally threaded ferrules clamped, glued, or otherwise secured to the end of the fiber in order to mount the fiber end in an internally threaded female socket or receptacle. Problems associated with this type of mount can include fiber twisting, xe2x80x9cz-gap attenuationxe2x80x9d, core pistoning, pullout forces, and strain on the fiber, which is often of relatively fragile, small-diameter construction.
The present invention is a two-piece termination ferrule for securing an optical fiber end to an internally-threaded female socket or receptacle. The ferrule virtually eliminates the problems associated with such mounting arrangements, first by strongly securing the fiber end inside an inner ferrule member formed to exacting tolerances, and then by securing the inner ferrule member to the female receptacle with an externally-threaded outer ferrule member that responds to being screwed into the female receptacle by clamping the exposed jacket of the fiber behind its connection to the inner ferrule member.
In a first embodiment of the invention, the inner ferrule member is a plug-like piece with a channel for receiving and securing the stripped end of an optical fiber. The front end of the inner ferrule member includes locating features that ensure proper positioning of the fiber end in a socket. The rear portion of the inner ferrule member contains the remainder of the stripped end of the fiber, and has a rear face whose diameter matches, at least approximately, that of the unstripped fiber jacket. The threaded outer ferrule member fits rotatably over the rear portion of the inner ferrule member, and takes the form of a partially split sleeve with orthogonal clamping portions and an external socket-matching thread whose diameter increases from front to back. The clamping portions extend rearwardly beyond the junction of the optical fiber jacket and the rear face of the inner ferrule member, and can be provided with teeth or similar projections capable of gripping the fiber jacket more securely. As the outer ferrule member is threaded into the female socket, the clamping sections are progressively forced together by the increasing diameter of the external thread to clamp both the inner ferrule member and the fiber jacket behind the inner ferrule member.
The first embodiment of the invention is useful for applications where minor rotation or twisting of the optical fiber toward the end of the insertion process is acceptable or readily compensated. This rotation tends to occur as the outer ferrule member""s clamping sections are squeezed down onto the fiber jacket during the last few turns, especially if gripping members or teeth bite into the jacket.
A second embodiment of the invention reduces the tendency of the fiber to twist as the outer ferrule member is screwed into the socket, and allows the fiber to untwist itself if minor twisting does occur. This is achieved by adding clamping members to the inner ferrule member, extending from the rear face to overlie and clamp the fiber jacket, and forming the bore of the outer ferrule member to rotate around and simultaneously squeeze the inner ferrule member""s clamping portions against the fiber jacket as the ferrule is threaded fully into the female socket. Gripping members or teeth can be formed on the inside of the inner ferrule member""s clamping portions to bite into and hold the fiber jacket more aggressively than orthogonal clamping action alone.
In both embodiments, the placement of jacket-clamping members over the fiber jacket behind the connection between the stripped end and the inner ferrule member relieves strain on the connection.
These and other features and advantages of the invention will be apparent from the following detailed description in light of the accompanying drawings.